Aromatic polyester resins such as polyethyleneterephthalate (PET) and polybutyleneterephthalate (PBT) have a wide variety of applications in the manufacture of molded goods, films, fibers and paints due to their excellent heat resistance, dimensional stability and mechanical properties.
Conventionally, the addition of silicones to these aromatic polyester resins had been considered in order to confer special properties such as mold-releasing properties, sliding properties and water repellency.
However, when dimethylsilicone oils were added to those polyester resins, although these oils had particularly good mold release and other properties, the resins often became cloudy or their surface properties were impaired due to the fact that the silicone and the resin had poor compatibility.
In order to remedy this defect, silicone compounds having improved compatibility with organic resins including polyester resins, obtained by modifying the compounds with phenyl groups, long chain alkyl groups or polyoxyalkylene groups, have been proposed (Japanese Tokko Sho 58-50064, Japanese Tokkai Sho 56-41256 and Japanese Tokko Hei 2-55459). However, although these silicone confounds have good compatibility with polyester resins, the retention of their properties, including mold-releasing properties, sliding properties and water repellency, was poor when they were added to the polyester resins.
Attempts have been made to improve the retention of these properties by adding reactive silicone oils having a group, such as --NCO, --COOH or an epoxy group, which reacts with the hydroxyl groups of the polyester resin. However, as the reaction requires the use of a catalyst or heat, the range of application of this method is limited.
Recently, studies have been performed on polyester-silicone copolymers consisting of a polyester and a silicone (Japanese Tokkai Hei 3-231812s Japanese Tokkai Hei 4-122726).
In those cases, although the aforementioned retention of properties is improved, the glass transition temperature of such a copolymer is very low, and this causes the loss of the inherent heat properties of the polyester resin.
As a result of intensive studies aimed at overcoming the aforementioned drawbacks, the inventors have discovered that when a polyester part which contains naphthalene rings is incorporated in a polyester-silicone copolymer the resulting copolymer can have a glass transition point raised up to at least 60.degree. C., and thereby the copolymer not only can retain the heat resistance of the polyester resin but also can possess various properties attributable to the silicone, including mold-releasing properties, sliding properties and water repellency, and these properties can be well retained over a period of time. These discoveries have led the inventors to formulate the present invention.